There are many situations when a mixable powder needs to be mixed with water. For example, powdered medicines, such as antibiotics, are mixed with sterile water in a medicine bottle. In another example, baby formula is added to sterile water in a baby bottle.
Many products and patents exist to enable these powders to be mixed. Some store the powders separately from the bottles or containers while others provide a two section bottle with a mechanism to add the powder to the liquid. One such mechanism breaks a barrier between the two sections, another pushes a surface out of the way.